The present invention relates to a film forming apparatus and method for forming a thin film such as a thin Ti film within a chamber and, more particularly, to a film forming apparatus and method in which a cleaning gas is supplied in the chamber after film formation for cleaning the interior of the chamber.
In semiconductor devices, metal-based thin films are used for, e.g., a metal wiring layer, a buried layer which is buried in a contact hole serving as a connection portion between a lower device layer and an upper wiring layer, or a via hole serving as a connection portion between upper and lower wiring layers, the buried layer electrically connecting the layers, and a two-layered barrier layer which is formed to prevent diffusion of an impurity prior to formation of the buried layer and made up of a Ti (titanium) film and a TiN (titanium nitride) film.
Such a metal-based thin film is generally formed using physical vapor deposition (PVD). In recent years, micropatterning of devices and a high integration degree are particularly demanded, and the design rule particularly becomes severer. Along with this, the line width and the opening diameter of the hole become more smaller. In addition, as the aspect ratio increases, the Ti film and the TiN film constituting the barrier layer are becoming difficult to reliably form at the hole bottom by PVD films.
The Ti film and the TiN film constituting the barrier layer are therefore formed by chemical vapor deposition (CVD) which is expected to form a higher-quality film. In general, to form the Ti film by CVD, TiCl.sub.4 (titanium tetrachloride) gas and H.sub.2 (hydrogen) gas are used as a reaction gas. To form the TiN film, TiCl.sub.4 gas, and NH.sub.3 (ammonia) gas or MMH (monomethylhydrazine) gas are used as a reaction gas.
When a thin film like the one described above is formed by CVD, a film is deposited on a semiconductor wafer serving as a substrate subjected to film formation, and deposits also attach to the inner wall of a chamber. For this reason, the interior of the chamber must be cleaned prior to next film formation. Recently, in this cleaning, the chamber wall and a susceptor are heated while ClF.sub.3 gas is introduced into the chamber to decompose the deposits, and the decomposition products are exhausted using a vacuum system with a vacuum pump.
If the ClF.sub.3 gas is used, TiF.sub.4 is produced as a by-product within the chamber, and the by-product attaches to the vacuum system. In the conventional method, therefore, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 8-176829, a portion of the vacuum system extending to the trap of a vacuum pipe is heated to a predetermined temperature to prevent TiF.sub.4 from attaching to the interior of the vacuum system.
A high-vacuum pump such as a drag pump is arranged at the front stage up to the trap of the vacuum pipe. In heating the vacuum pipe, the high-vacuum pump is also heated. If the pump is heated to such a high temperature as to prevent TiF.sub.4 from attaching, the rotor of the high-vacuum pump may be creep-ruptured.
To solve this problem, the trap may be arranged at the front stage of the high-vacuum pump to avoid the heating of the high-vacuum pump. By this method, however, the high-vacuum pump must have a large capacity, and vapor generated from the trap may influence the chamber.